Healing and sealing carbon nanotubes--growth and closure within a transmission electron microscope.

The growth of carbon nanotubes, and the role of the catalyst in this process, is only partially understood. Here we report real-time TEM observations of a partially embedded crystalline catalyst particle retracting from the hollow of a growing carbon nanotube, followed by a subsequent closure of the tube. The retraction is explained by size-dependent capillary forces, demonstrating the importance of capillary forces in the interaction between the catalyst and the nanotube. The observed crystallinity of the particle provides evidence that carbon nanotube growth in these circumstances does not require a molten catalyst, and closure of the tube suggests a carbon concentration gradient is involved in the growth.